08 Fakultät Mathematik und Physik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9
Browse
Item Open Access Experimental results on absolute phonon detection sensitivity of superconducting tunneling junctions(1972) Trumpp, Hans-Joachim; Epperlein, Peter W.; Lassmann, KurtSuperconducting tin tunnelling junctions are used for generating and detecting 300 GHz phonons. The absolute phonon detection sensitivity can be obtained, making possible a comparison of the number of phonons detected to the number of phonons generated. This, together with measurements of the dependence of junction time constant on its thickness, gives an indication that far more phonons are radiated into liquid He than is expected from a simple acoustic model.Item Open Access Emission of high frequency relaxation phonons by superconducting aluminium tunneling junctions(1972) Welte, Michael; Lassmann, Kurt; Eisenmenger, WolfgangUp to now the emission of relaxation phonons of energy E > 2 Δ by tin tunnelling junctions could not be observed by reason of the strong reabsorption of such phonons in the generator junction. We now report experiments in which the emission of relaxation phonons of energy E > 2 Δ by aluminium tunnelling junctions is observed. The conditions necessary for the emission of high frequency relaxation phonons are discussed.Item Open Access Transition of 280 GHz phonons from superconducting tunneling junctions into liquid helium and silicon(1972) Trumpp, Hans-Joachim; Lassmann, Kurt; Eisenmenger, WolfgangComparative phonon emission experiments carries out in liquid helium and vacuum with superconducting tin-tin tunneling junctions evaporated on silicon crystals, show a transmission into helium about three times higher than the transmission into silicon.Item Open Access Evidence for 870 GHz phonon emission from superconducting Al tunnel diodes through resonant scattering by oxygen in silicon(1973) Forkel, Werner; Welte, Michael; Eisenmenger, WolfgangThin-film aluminum superconducting tunnel junctions can be used to generate phonons up to 10 12 Hz. This is substantiated by the observation of the 29-cm -1 absorption line of O 16 impurities in silicon, so far only known from infrared spectra.Item Open Access Transmission of heater generated high frequency phonons through a sapphire-He II boundary(1974) Buck, Jochen; Lassmann, Kurt; Eisenmenger, WolfgangWe report on a new method to measure the absolute transmission coefficient through a solid-He II-boundary by determining absolutely the temperature amplitude of the second sound pulses in the liquid.Item Open Access Phononenphysik mit supraleitenden Tunnelkontakten(1974) Eisenmenger, WolfgangWeitere Methoden zur Erzeugung und zum Nachweis höchstfrequenter mechanischer Wellen (auch Gitterschwingungen oder Phononen genannt) werden in diesem Aufsatz behandelt. Zur Erzeugung von Phononen mit Frequenzen größer 10 11 Hz kann man auch die Elektron-Phonon-Wechselwirkung in Metallen oder Supraleitern ausnutzen. Im Prinzip wird dabei den Elektronen aus einer Batterie Energie zugeführt, die dann als Phononenemission an das Gitter abgegeben wird. Phonon-Übergänge in Supraleitern sind dabei wegen der speziellen energetischen Struktur der Elektronenzustände (Energielücke) von besonderem Interesse.Item Open Access Phonon emission spectra of thin metallic films(1975) Frick, Wolfgang; Waldmann, Dieter; Eisenmenger, WolfgangThin metallic films evaporated on an Al 2 O 3-single crystal and cooled to liquid helium temperatures are heated by short electric current pulses. The high frequency part of the emitted phonons is detected by calibrated superconductive tunneling junctions on the opposite surface of the substrate. The observed phonon detector signal amplitude is compared with theoretical models taking account of the boundary conditions for elastic waves in the film. It is found that the phonon spectrum emitted perpendicularly to the substrate-film boundary depends strongly on the thickness of the heater film.Item Open Access Quasiparticle recombination and 2Δ-phonon-trapping in superconducting tunnelling junctions(1976) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, RichardThe experimental recombination lifetime τeff of quasiparticles in superconducting films in general exceeds the intrinsic recombination lifetime τR by phonon trapping. On the basis of geometric acoustic propagation and reabsorption of phonons emitted in quasiparticle recombination, τeff is calculated as a function of film thickness d taking into account longitudinal and transverse phonon reabsorption, bulk loss processes and acoustical phonon transmission into the substrate. With increasing thickness d three characteristic ranges are found: range 1 with film thickness d small compared to the phonon reabsorption mean free path Λw, range 2 with d larger than Λw and dominating boundary losses, and range 3, also with d larger than Λw but with dominating bulk losses. For very small d the relation between τeff and τR, the intrinsic recombination lifetime, contains only the limiting angle of total reflection of phonons within the superconducting film. Therefore, τR can be directly obtained by τeff measurements and from the sound velocities of the film-substrate system. Range 2 is characterized by a linear dependence of τeff on d. In this range it is not possible to obtain τR from τeff measurements, however, τeff allows a determination of the phonon boundary transmission. Range 3 shows no thickness dependence of τeff on d in the limit of large d values. In this range a further method for obtaining τR from τeff values is suggested.Item Open Access Anisotropy of phonon emission from hot electrons in germanium(1976) Reupert, Wolfram; Lassmann, Kurt; Groot, Peter deWe have measured quantitatively the anisotropy of the electron-acoustical phonon scattering in n-germanium in five directions of the (lTO) plane utilizing tunneling junctions for calibrated detection of the phonon radiation emitted from a small avalanche breakdown region in the germanium surface. For comparison and evaluation of phonon focusing a constantan heater and a tunneling junction were also used as phonon sources. A similar experiment has been reported by A. Zylbersztejn, but he could only compare the ratio of the amplitudes of longitudinal and transverse phonon pulses in a given crystal direction to the calculation.Item Open Access Superconducting tunnelling junctions as phonon generators and detectors(1976) Eisenmenger, WolfgangIt is the aim of this chapter to review the experimental and theoretical results obtained by the use of superconducting tunneling junctions as phonon generators and detectors. We first discuss the fundamental processes and their experimental evidence in more qualitative terms in Sections II and III. The quantitative treatment of phonon detection and generation is given in Sections IV and V, while Section VI discusses phonon spectroscopy and other applications.Item Open Access Phonon scattering due to deep acceptors in semiconductors(1976) Combarieu, Andre de; Lassmann, KurtWe have measured the magnetothermal conductivity in GaAs(Mn) and Si(In) for temperatures between 1.4 K and 90 K at magnetic fields up to 8 T. In both cases the dopants are deep acceptors with binding energy much larger (110 meV and 165 meV respectively) than given by the effective mass theory (~ 35 meV). There is a double interest in such systems: First, an excited level 3 meV (4.2 meV) above the acceptor ground state has been concluded from ultrasonic measurements. Such an excited state might be connected with a Jahn-Teller effect of these deeper acceptors and should be seen by resonant phonon scattering in thermal conductivity. Second, an anomalous behavior of the magnetothermal conductivity has been found for shallowacceptors in Ge (but not in Si) making comparison with systems with different g-factors desirable. The g-factors of acceptors in GaAs are roughly three times, the g-factor of Si(In) about 0.6 times that of Si(B).Item Open Access Ultrasonic attenuation due to the neutral acceptor indium in silicon(1976) Schad, Hanspeter; Lassmann, Kurt-Item Open Access Analysis of the acoustlc transients in the pulse response of the linear electro-optic effect(1976) Veeser, Hermann; Bogner, Udo; Eisenmenger, WolfgangThe pulse response of the linear electro-optic effect is investigated with high temporal and spatial resolution in KDP, KD*P, and biaxial LiCOOH · H2O. Experimental results, which are explained theoretically, show that the piezo-optic transients induced by the piezoelectric effect, are generated by stress release waves. Starting from the surfaces, these excite by reflection, diffraction, and superposition, due to the finite crystal dimensions, normal vibration modes too. It is shown that the direct electro-optic effect can be measured for all crystal classes at the beginning of the pulse response. The pulse method also yields static electro-optic, piezo-optic, and elastic constants. The values of r63, r63, p66 and c66 measured in KDP, agree well with those of other authors. Measurement of the direct electro-optic effect of LiCOOH · H2O in some directions yields values within 1 to 4 × 10-12 m/V.Item Open Access High frequency phonon emission from superconducting Al-tunnelling junctions(1976) Eisenmenger, WolfgangIn single particle tunneling between identical superconductors phonons are generated by relaxation - and recombination transitions of injected quasiparticles. Phonon detection is mediated by the breaking of Cooper-pairs by phonons with energy exceeding the superconducting energy gap 2Δ D. This leads to an increase of the quasiparticle population and a corresponding contribution to the tunneling current in the thermal tunneling regime 0Item Open Access Energy gap reduction in superconducting tin films by quasiparticle injection(1977) Fuchs, Jürgen; Epperlein, Peter W.; Welte, Michael; Eisenmenger, WolfgangIn Sn-/-Sn-/-Pb tunneling structures the energy gap ΔSn of Sn is reduced by quasiparticle injection via single-particle tunneling between the Sn films. ΔSn as function of the quasiparticle density is probed by the Pb contact and found in agreement with the theory of Owen and Scalapino. An instability of the energy gap of Sn is observed at the critical gap reduction ratio predicted by this theory for a first-order phase transition.Item Open Access Intrinsic and experimental quasiparticle recombination times in superconducting films(1977) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, RichardExperimental quasiparticle recombination lifetime data for superconducting Al, Sn, and Pb films are compared with calculations based on a ray acoustic model taking account of the film thickness dependence of the reabsorption of recombination phonons. Information on the true or intrinsic quasiparticle recombination lifetime obtained from these and other data is discussed.Item Open Access Sources of loss processes in phonon generation and detection experiments with superconducting tunneling junctions(1977) Trumpp, Hans-Joachim; Eisenmenger, WolfgangObserving the phonon yield, i.e. the ratio of the experimental phonon signal amplitude and the corresponding calculated value, phonon losses within the generation-detection system can be localized and determined quantitatively. With tin junctions on pure silicon substrates immersed in liquid helium the phonon yield is 3–5%. Under vacuum conditions the yield rises to 10–12% indicating strong phonon transmission to the helium bath. The experimental lifetime for 280 GHz phonons in the silicon substrate is longer than 65 µs indicating negligible volume losses and losses at the free substrate surface. It is further shown, that volume losses inside the phonon generator and detector are small compared to the total loss of about 90%. By phonon reverberation measurements we find evidence that the main sources for phonon losses are localized at the boundaries of the tunneling junctions to the substrate. This is supported by an increase of the phonon yield with improved polishing from about 9% (mechanical), 10% (chemical) to 12% (sputter etching). A SIMS analysis indicates the presence of carbonhydrates and probably of water in the boundaries. This layer of extraneous molecules together with the nonideal surface structure of the substrate and the evaporated films weakens the mechanical bonding between the tunnel junctions and the substrate and is possibly causing strong phonon splitting by anharmonic forces.Item Open Access Reflection of high frequency phonons at free silicon surfaces(1978) Marx, Dieter; Buck, Jochen; Lassmann, Kurt; Eisenmenger, WolfgangIn reflection experiments at free silicon [100]-surfaces we could distinguish between specularly and diffusely reflected transverse phonons propagated along <100>-directions. With increasing phonon frequency the number of diffusely scattered phonons increase relative to that of specularly reflected phonons.Item Open Access Effective quasiparticle recombination times and electronic density of states at the Fermi level in superconducting films(1978) Epperlein, Peter W.; Lassmann, Kurt; Eisenmenger, Wolfgang-Item Open Access Quasiparticle recombination time in superconducting tin and normal electronic density of states at the Fermi surface from tunnel junction experiments(1978) Epperlein, Peter W.; Lassmann, Kurt; Eisenmenger, WolfgangWe have measured the temperature dependence of the effective quasiparticle recombination time in superconducting tin tunnel junctions by current and laser pulse excitation. The experimental times show satisfactory agreement with calculations based on the ray acoustic lifetime model of Eisenmenger et al. taking into account the film thickness dependence of the phonon reabsorption, 2Delta-phonon volume loss processes and phonon transmission from the junction into the substrate and liquid helium. On the basis of the BCS density of thermally excited quasiparticles and simplified rate equations for quasiparticle recombination, and from the analysis of measurements of decaying excess quasiparticle concentrations we obtain a mean valueN 0=(2.73±0.03) 1022 eV-1 cm-3 for the electronic density of states at the Fermi Surface in thin, evaporated tin films. This value differs less than 5% from that obtained from the experimental electronic heat-capacity coefficient of the bulk material.